As a technique for recording and/or reproducing digital data, there is a data recording technique employing, as a recording medium, an optical disc, inclusive of a magneto-optical disc, such as CD (Compact Disc), MD (Mini-Disc) or DVD (Digital Versatile Disc). The optical disc is a generic term of the recording medium comprising a disc of a thin metal sheet protected with plastics. The disc is illuminated by laser light and a signal is read out in terms of changes in the reflected laser light.
The optical disc may be classified into a read-only type, such as CD, CD-ROM or DVD-ROM, and a recordable type, allowing a user to record data thereon, such as MD, CD-R, CD-RW, DVDR, DVD-RW, DVD+RW or DVD-RAM. The recordable type disc allows for data recording by exploiting the magneto-optical recording system, a phase change recording system or a dye film change recording system. The dye film change recording system, also termed a write-once recording system, allows for data recording only once, while it does not allow for data rewriting. Thus, the dye film change recording system may conveniently be used for data saving. The magneto-optical recording disc or the phase change recording system allows for data rewriting and may be used for various application, including, first of all, recording various contents data, such as music, pictures, games or application programs.
Recently, a high-density optical disc, termed the Blu-ray Disc, has been developed to increase the recording capacity significantly.
This high-density disc records and/or reproduces data under a condition of the laser light with a wavelength of 405 nm (so-called blue laser) and an objective lens with the NA equal to 0.85. A data block of 64 kB (kilo-bytes) is used as a recording reproducing unit, with the track pitch of 0.32 μm and a line density of 0.12 μm/bit. If the format efficiency is 82%, a data volume of 23.3 GB (gigabytes) may be recorded and/or reproduced on a disc with a diameter of 12 cm.
With this high-density disc, a write-once type or a rewritable type has been developed.
For recording data on a recordable disc, such as a disc of the magneto-optical recording system, a dye film change recording system or a phase change recording system, it is necessary to provide a guide for tracking relative to a data track. To this end, a groove is formed from the outset as a pre-groove and the groove or a land (a part with a trapezoidal cross-section, defined between neighboring grooves) is used as a data track.
It is also necessary to record the address information to allow for data recording at a preset location on the data track. This address information is sometimes recorded by wobbling (meandering) the groove.
That is, the sidewall of a track, formed as a pre-groove for data recording, is wobbled in agreement with the address information.
In this case, the address can be read out from the wobbling information, obtained as the reflected light information during recording or reproduction, such that data may be recorded or reproduced for a desired location even if no pit data representing the address is pre-formed on the track.
The absolute time (address) information, represented by the wobbled groove, is termed the ATIP (Absolute Time In Pregroove) or ADIP (ADdress In Pregroove).
In such data-recordable recording medium (which is not read-only), there is known a technique providing an exchange area to exchange data recording positions on the disc. This technique is a defect management technique allowing optimum recording and/or reproduction by providing an exchange recording area which takes the place of a defect area unsuitable for data recording, such as a flaw, if such defect is present on the disc.
Meanwhile, if attention is directed to a write-once type optical recording medium, which allows recording only once, such as CD-R, DVD-R or a high density disc, such write-once type optical recording medium suffers from various constraints, because no data can be recorded on a prerecorded area.
In particular, in the write-once recording medium, the technique of updating the management information responsive to the data recording poses a problem.
That is, as a usual practice, the management information must be properly updated responsive to the recording of user data. On the other hand, management of the recording state of the user data based on the management information helps improve the processing speed in writing data on a disc or reading data from the disc.
However, with the write-once recording medium, it is not proper to update the management information each time user data is recorded on the recording medium, because the area for recording the management information is consumed excessively.
Considering that limitations are imposed on the size of the recording area for the management information, certain preset conditions need to be imposed on the recording of the management information on the disc.
For example, in the DVD-R, the management information, updated in the recording apparatus responsive to data recording, is recorded on the disc, subject to the write volume of the user data surpassing a preset volume.
Under these conditions, there is a time lag until the management information recorded on the disc is rewritten to a state reflecting the latest recording state of the user data actually recorded on the disc. That is, there is a time period during which the management information recorded on the disc does not reflect the recording state of the user data on the disc.
If, due to supply interruption, power down by the user operation or failure in writing, the management information cannot be properly updated on the disc, the management information is unmatched to the user data on the disc, such that unmanageable user data, that is, non-reproducible user data, is produced.
For preventing this from occurring, a variety of techniques have been proposed for holding the management information, even on power down, using e.g. a non-volatile memory, to enable the management information to be updated later on the disc, or to verify the non-matching between the management information and the user data on the disc to effect restoration processing, as described for example in the following Patent Publication 1:
[Patent Publication 1] Japanese Patent Application Laid-Open No. 2002-3122940
Meanwhile, in a recordable disc, the last address of the user data (last recording position information specifying the last position of recording of the user data) is sometimes provided as such one management information. This last address is termed the LRA (last recorded address), as an example. This last address is that of the area where user data has been written on the disc.
In the write-once optical disc, the usual practice is to pad user data sequentially from the leading end of the user data area for recording. Thus, in newly recording data, it is sufficient to record the data as from an address (LRA+1) next following the address LRA.
If it is desired to record data as from an address further in rear of LRA+1, such a technique is needed which consists in writing dummy data, such as zero data, for a domain as from the address LRA+1 to a recording start address, or registering the domain as an unrecorded area.
Meanwhile, the reason the data is padded sequentially from the inner rim of the write-once disc is that the conventional optical recording disc has been developed on the basis of a ROM type disc and hence replay cannot be made if there is an unrecorded area on the disc.
These circumstances impose limitations on the random access recording on the write-once recording medium.
In order to render a write-once disc more accessible at random, the present inventors have proposed in an international application (filing number: JP04/003212) such a technique consisting in providing the written/unwritten indicating information (space bitmap information) indicating whether or not data has been written, from one data unit in the recording area to another, as the management information, to enable a recorded area and a non-recorded area to be verified by this written/unwritten indicating information.
This enables data to be recorded in a desired address in a write-once disc, without being limited to sequentially padding the data for recording. It is then unnecessary to record dummy data to expedite the write processing and to reduce the processing load on the device.
However, even with the system exploiting the space bitmap, proper updating of the management information (space bitmap or LRA) on the disc poses a problem. That is, there is a demand for proper management information write processing whereby not only the management area on the disc is not wastefully consumed but also the time period of non-matching between the management information and the state of recording of the user data is not protracted excessively.
There is a also demand for facilitated setting of the matched state even in case the management information on the disc and the state of recording of the user data has become non-matched due to e.g. the power down of the device.
In this respect, there is a technique of holding the management information to be written on the disc by exploiting the conventional non-volatile memory. However, there is also a demand for a system not employing the non-volatile memory because the current non-volatile memory suffers from limitations on the number of times of data update events and hence is not suitable for recording frequently updated data.